Serbia and Kosovo have agreed to work together to patrol their common border.

The two sides reached the agreement in Brussels late on December 2.

"The parties will gradually set up the joint, integrated, single and secure posts at all their common crossing points," a statement from the EU, which mediated the discussions, said.

The breakthrough came hours after German Chancellor Angela Merkel said Serbia was not ready for EU membership.

Speaking to parliament, Merkel said Serbia could only join the EU "through the normalization of its relations with Kosovo," and that "Serbia has so far not lived up to these expectations sufficiently."

Unrest between NATO troops and ethnic Serbs in northern Kosovo near the border with Serbia has flared up in recent weeks.

Thirty German and Austrian soldiers have been hurt in clashes in northern Kosovo over the past week.

Trouble began in July when Serbs erected dozens of roadblocks after the government of Kosovo said it would man border posts in the mainly Serb north.

Many Serbs who live there reject Kosovo's 2008 declaration of independence from Serbia.